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Today's Topics:
1. eve / did = 0.talktalktalk... (Alexander.Vladislav.Popov )
2. Trying to compile my first program that imports another
program (Mitchell Kaplan)
3. Re: Trying to compile my first program that imports another
program (MAN)
4. Re: Trying to compile my first program that imports another
program (Dean Herington)
----------------------------------------------------------------------
Message: 1
Date: Thu, 22 Apr 2010 16:12:24 +0600
From: "Alexander.Vladislav.Popov "
<[email protected]>
Subject: [Haskell-beginners] eve / did = 0.talktalktalk...
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Dear Everebody.
Hepl me please to parallelize (parallel computing of evedidtalk
function) the rebus:
-- | eve / did = 0.talktalktalk...
ten :: Integral a => [a]
ten = [0..9]
infixr 7 /:
(/:) :: (Integral a) => [a] -> [a] -> [a]
(/:) [] _ = [0]
(/:) _ [] = []
(/:) x y = coldiv (getInteger x) (getInteger y)
getInteger :: (Num a) => [a] -> a
getInteger = foldl ((+) . (*10)) 0
coldiv :: (Integral a) => a -> a -> [a]
coldiv a b = q : if r == 0
then []
else coldiv (r * 10) b
where
(q, r) = a `quotRem` b
evedidtalk = [ ([e, v, e], [d, i, d], [t, a, l, k]) |
e <- ten,
v <- ten, v /= e,
d <- ten, d /= e, d /= v,
i <- ten, i /= e, i /= v, i /= d,
t <- ten, t /= e, t /= v, t /= d, t /= i,
a <- ten, a /= e, a /= v, a /= d, a /= i, a /= t,
l <- ten, l /= e, l /= v, l /= d, l /= i, l /= t, l /= a,
k <- ten, k /= e, k /= v, k /= d, k /= i, k /= t, k /= a, k /=
l,
take 9 ([e, v, e] /: [d, i, d]) == [0, t, a, l, k, t, a, l, k]
]
Sincerely, Alexander
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Message: 2
Date: Sun, 25 Apr 2010 21:07:36 -0400
From: "Mitchell Kaplan" <[email protected]>
Subject: [Haskell-beginners] Trying to compile my first program that
imports another program
To: <[email protected]>
Message-ID: <84f7441dd51d4ca6bd9d2dc380a88...@home93f2a7f3c6>
Content-Type: text/plain; charset="us-ascii"
Hi,
I created (with help) a function to test for prime numbers. It worked well
enough for now in ghci.
----------------
f x n y
| n>y = True
| rem x n == 0 = False
| otherwise = f x (n+1) y
primeQ x = f x 2 y
where
y = floor(sqrt(fromIntegral x))
---------------
I then wanted to create object code so that I could import it. It seemed
that I had to precede the above with the 2 lines:
----------------
module Prime
where
----------------
I ran:
ghc -c prime.hs, and created prime.o and prime.hi.
Next, I wanted to write a program to import and use this function.
I wrote:
------------
module Main () where
import Prime
main = primeQ 123
------------
I tried to compile this with:
ghc -o test Main.hs prime.o
I got the following error:
Main.hs:5:0:
Couldn't match expected type 'IO t' against inferred type 'Bool'
In the expression: main
When checking the type of the function 'main'
----------------
First I'd like a hint as to what I need to do to make this work.
It's pretty obvious that I don't know what I'm doing with regard to types.
Also, I have no idea if I have to name this module Main, but when I didn't
the compiler complained about that.
In the function that I think I had to re-write to make object code, I wound
up with 2 where statements, which worries me.
I'd really appreciate any help in getting me unraveled.
Mitchell
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------------------------------
Message: 3
Date: Sun, 25 Apr 2010 22:25:32 -0300
From: MAN <[email protected]>
Subject: Re: [Haskell-beginners] Trying to compile my first program
that imports another program
To: Mitchell Kaplan <[email protected]>
Cc: [email protected]
Message-ID: <1272245132.4137.9.ca...@dy-book>
Content-Type: text/plain; charset="UTF-8"
Hi, Mitchell
First of all, you don't really need to compile your module Prime to be
able to import it. Supposing you just want to, though:
Your funcion primeO is 'pure', it work on numbers only, and will return
the same results for the same arguments every time, without "launching
missiles" or side-effects of any kind.
The main function (in the Main module), which is the 'main entry
point' (like in C), is of type 'IO ()' ... this means a lot, and you
should really look into types for Haskell; but in a nutshell, it means
the function 'main' may have side-effects (like printing to stdout, or
opening a socket, deleting a file, etc) which cannot be predicted.
Haskell is very careful as to keep pure code pure, and non-pure code,
well, non-pure... [check out 'monads']. The 'main' function is of type
'IO ()', so all functions called by it must have type 'IO something'.
[IO is a monad]. Your function prime0 is of type 'Bool', so you need to
inject it into the 'IO' [get it into the monad]. This is done with the
function 'return' (which is quite different to that of C):
module Main where
import Prime
main = return (primeQ 123)
BTW, your Haskell program must have a Main module. You will write your
modules with "module SomeThing where", and name that file SomeThing.hs;
the Main module can have any filename you want, though.
El dom, 25-04-2010 a las 21:07 -0400, Mitchell Kaplan escribió:
> Hi,
>
>
>
> I created (with help) a function to test for prime numbers. It worked
> well enough for now in ghci.
>
>
>
> ----------------
>
> f x n y
>
> | n>y = True
>
> | rem x n == 0 = False
>
> | otherwise = f x (n+1) y
>
>
>
> primeQ x = f x 2 y
>
> where
>
> y = floor(sqrt(fromIntegral x))
>
> ---------------
>
>
>
> I then wanted to create object code so that I could import it. It
> seemed that I had to precede the above with the 2 lines:
>
>
>
> ----------------
>
> module Prime
>
> where
>
> ----------------
>
>
>
> I ran:
>
> ghc âc prime.hs, and created prime.o and prime.hi.
>
>
>
>
>
> Next, I wanted to write a program to import and use this function.
>
>
>
> I wrote:
>
>
>
> ------------
>
> module Main () where
>
> import Prime
>
> main = primeQ 123
>
> ------------
>
>
>
> I tried to compile this with:
>
> ghc âo test Main.hs prime.o
>
>
>
> I got the following error:
>
> Main.hs:5:0:
>
> Couldnât match expected type âIO tâ against inferred type
> âBoolâ
>
> In the expression: main
>
> When checking the type of the function âmainâ
>
> ----------------
>
>
>
> First Iâd like a hint as to what I need to do to make this work.
>
>
>
> Itâs pretty obvious that I donât know what Iâm doing with regard to
> types. Also, I have no idea if I have to name this module Main, but
> when I didnât the compiler complained about that.
>
>
>
> In the function that I think I had to re-write to make object code, I
> wound up with 2 where statements, which worries me.
>
>
>
> Iâd really appreciate any help in getting me unraveled.
>
>
>
> Mitchell
>
>
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 4
Date: Mon, 26 Apr 2010 01:06:09 -0400
From: Dean Herington <[email protected]>
Subject: Re: [Haskell-beginners] Trying to compile my first program
that imports another program
To: MAN <[email protected]>, Mitchell Kaplan
<[email protected]>
Cc: [email protected]
Message-ID: <a06240800c7facea12...@[192.168.1.100]>
Content-Type: text/plain; charset="iso-8859-1" ; format="flowed"
MAN's nutshell explanation is good, and his
rewrite of the Main module is type-correct. But
note that the result of the `main` action (of
type IO t for some type t) is deliberately
discarded, so you probably want something more
useful, such as:
module Main where
import Prime
main = print (primeQ 123)
Dean
At 10:25 PM -0300 4/25/10, MAN wrote:
>Hi, Mitchell
>
>First of all, you don't really need to compile your module Prime to be
>able to import it. Supposing you just want to, though:
>
>Your funcion primeO is 'pure', it work on numbers only, and will return
>the same results for the same arguments every time, without "launching
>missiles" or side-effects of any kind.
>
>The main function (in the Main module), which is the 'main entry
>point' (like in C), is of type 'IO ()' ... this means a lot, and you
>should really look into types for Haskell; but in a nutshell, it means
>the function 'main' may have side-effects (like printing to stdout, or
>opening a socket, deleting a file, etc) which cannot be predicted.
>
>Haskell is very careful as to keep pure code pure, and non-pure code,
>well, non-pure... [check out 'monads']. The 'main' function is of type
>'IO ()', so all functions called by it must have type 'IO something'.
>[IO is a monad]. Your function prime0 is of type 'Bool', so you need to
>inject it into the 'IO' [get it into the monad]. This is done with the
>function 'return' (which is quite different to that of C):
>
>module Main where
>import Prime
>main = return (primeQ 123)
>
>BTW, your Haskell program must have a Main module. You will write your
>modules with "module SomeThing where", and name that file SomeThing.hs;
>the Main module can have any filename you want, though.
>
>
>El dom, 25-04-2010 a las 21:07 -0400, Mitchell Kaplan escribió:
>> Hi,
>>
>>
>>
>> I created (with help) a function to test for prime numbers. It worked
>> well enough for now in ghci.
>>
>>
>>
>> ----------------
>>
>> f x n y
>>
>> | n>y = True
>>
>> | rem x n == 0 = False
>>
>> | otherwise = f x (n+1) y
>>
>>
>>
>> primeQ x = f x 2 y
>>
>> where
>>
>> y = floor(sqrt(fromIntegral x))
>>
>> ---------------
>>
>>
>>
>> I then wanted to create object code so that I could import it. It
>> seemed that I had to precede the above with the 2 lines:
>>
>>
>>
>> ----------------
>>
>> module Prime
>>
>> where
>>
>> ----------------
>>
>>
>>
>> I ran:
>>
>> ghc -c prime.hs, and created prime.o and prime.hi.
>>
>>
>>
>>
>>
>> Next, I wanted to write a program to import and use this function.
>>
>>
>>
>> I wrote:
>>
>>
>>
>> ------------
>>
>> module Main () where
>>
>> import Prime
>>
>> main = primeQ 123
>>
>> ------------
>>
>>
>>
>> I tried to compile this with:
>>
>> ghc -o test Main.hs prime.o
>>
>>
>>
>> I got the following error:
>>
>> Main.hs:5:0:
>>
>> Couldn't match expected type 'IO t' against inferred type
>> 'Bool'
>>
>> In the expression: main
>>
>> When checking the type of the function 'main'
>>
>> ----------------
>>
>>
>>
>> First I'd like a hint as to what I need to do to make this work.
>>
>>
>>
>> It's pretty obvious that I don't know what I'm doing with regard to
>> types. Also, I have no idea if I have to name this module Main, but
>> when I didn't the compiler complained about that.
>>
>>
>>
>> In the function that I think I had to re-write to make object code, I
>> wound up with 2 where statements, which worries me.
>>
>>
>>
>> I'd really appreciate any help in getting me unraveled.
>>
>>
>>
> > Mitchell
------------------------------
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